If you got rid of timezones, you’d still end up creating it in all but name since the vast majority of business will be occurring during daytime hours around the world. For example, an office in Tokyo sending emails to their NYC office at 0800 UTC (currently 0400 EDT in NYC) wouldn’t end up getting answered for at least 3-4 hours when those employees started logging in. In other words, people would still be doing calculations in their heads to know when business hours are in that region, essentially recreating timezones.
Not necessarily. In Teams, it shows the user’s specific hours they work as well as the time difference (this person is 2 hours behind you). All it would need is to remove the time difference and just display the time they work.
A person in Japan would just put in their signature or it would be in the application that they work from 0400 to 1200 while you still work 0800 to 1600 and you’d have your answer.